Due to the hierarchical nature of high-temperature hydrocarbon oxidation, modeling the combustion chemistry of higher hydrocarbon fuels typically requires a fuel-specific reaction model that describes the fragmentation of the fuel into small species, and a foundational fuel chemistry model that describes the oxidation of these species. Shared by the combustion of large hydrocarbons, the foundational fuel chemistry is also the rate-limiting step and therefore a crucial part for constructing reliable combustion models for any higher hydrocarbons. The talk examines the aforementioned problems from both ends. The Foundational Fuel Chemistry Model (FFCM) is an effort directed at developing a reliable combustion model for the foundational fuels with rate parameters optimized and uncertainty minimized. The first version, FFCM-1,optimized for H₂,​H​₂/​CO,CH_​2O​ and CH​₄ combustion,was constrained with carefully evaluated fundamental combustion data. The model reconciles all the experimental targets chosen and has significantly reduced prediction uncertainties. The remaining kinetic uncertainties in FFCM-1 were further analyzed with extinction and ignition residence time predictions in perfectly-stirred reactor conditions to examine the critical remaining kinetic uncertainties in FFCM-1. The optimization and uncertainty quantification procedures were also extended to include the optimization of activation energies. As a single-component large-fuel example, JP10 was studied using the Hybrid Chemistry (HyChem) approach, which assumes a decoupled fuel pyrolysis and oxidation of pyrolysis products. The pyrolysis model is described with highly-lumped steps and optimized against experimental data from shock tube and flow reactor measurements. The model performance will be discussed.